In recent years, the contents of music, visual images, books, etc. which are converted to digital data, i.e. digital contents have been in widespread use through various storage media and communication links such as the Internet. In connection with this, copyright infringements such as unauthorized copying have also increased since the digital contents are, as digital data, not deteriorated through copying.
To prevent the unauthorized copying of digital contents, there is a known method of prevention by including a flag which indicates prohibition/permission of copying in the data. However, this method has such defects that an apparatus which can ignore flags enables to carry out unauthorized copying, and the users are disallowed to produce the backup copies of personally possessing data.
To eliminate these defects, for instance, Japanese Laid-Open Patent Application No. 11-272565/1999 (Tokukaihei 11-272565; published on Oct. 8, 1999) discloses a technique to control the reproduction of digital contents using IDs uniquely assigned to respective devices for reproducing the digital contents. With this technique, a digital content includes a device ID which specifies the device permitted to reproduce the digital content, and a device for reproducing the digital content reads out the device ID of the digital content so that the reproduction of the digital content is carried out only when the device ID which has been read out corresponds to the device ID of the device.
According to this technique, it is possible to prevent unauthorized copying in the following manner: When, for instance, purchasing a digital content from a content sales server on the Internet, a customer notifies the device ID of his/her own device to the content sales server along with the content that he/she wants, thereby purchasing the content by downloading the same. The digital content that has been purchased in this way includes a device ID. Thus if he/she copies the content and gives it to a friend, the reproduction of the copied content is not allowed in the device of the friend. In this wise, even if one produces the unauthorized copy of a digital content, the copied content can only be reproduced in his/her own device and hence unauthorized copying is practically prevented.
Now, considering the case to realize the technique of Japanese Laid-Open Patent Application No. 11-272565/1999 as software for general-purpose computers, in order to avoid the overlapping of device IDs between devices, device IDs are determined using information unique to the respective computers. When a computer does not store any information unique to the same or the information unique to the computer is not available, there is such a conceivable option that a device ID is determined by generating random numbers on the occasion of installing the software.
However, when, for instance, the OS (Operating System) or the content player of a computer is out of order, it may be necessary to reinstall the software. If the OS or the content player is reinstalled, another device ID is determined and consequently the computer is no longer allowed to reproduce the digital contents that have previously been purchased.
The present invention is worked out to solve the foregoing problem, so that the objective of the present invention is to provide a communication system, a terminal device, a reproduction program, a storage medium storing the reproduction program, a server machine, a server program, and a storage medium storing the server program, by which a device ID based on which the terminal device reproduces digital contents can be recovered, when the device ID is altered due to reasons such as the anomaly of the device.